X-ray inspection in the food industry

Why X-rays? X-rays can penetrate materials that do not allow any visible light to pass through. Impurities hidden in food, such as glass, bone, stones or even system components, become visible as a result of an X-ray inspection because they absorb more X-rays than the surrounding food.

Reasonable costs for using X-ray scanners for food inspection are pitted against incalculable risks if products are not adequately quality assured – and if, as a result, the company’s reputation is battered due to defective products, the customer’s confidence is damaged or it even becomes necessary to initiate expensive, high-profile recall campaigns.

X-ray inspection systems in worldwide use

WIPOTEC-OCS X-ray scanners for the inspection of food have gained acceptance worldwide. Product inspection is the manufacturers responsibility. The procedures in food inspection are becoming more and more demanding due to increases in processing speeds and new performance requirements. In many cases, it’s not just about detecting foreign bodies. With ready meals in trays, a quantity and completeness check may be added to foreign body detection or it may be necessary to check a heat-sealed seam.

Thanks to their slim designs and high modularity in respect of their core components, different equipment versions and inbound-outbound components, WIPOTEC-OCS X-ray information systems are very easily integrated into production lines. The balcony architecture combined with the C-shaped product space and chamfered surfaces enable quick, easy and thorough cleaning. All X-ray scanners therefore meet the highest hygiene requirements.

Modular X-ray technology from WIPOTEC-OCS

WIPOTEC-OCS X-ray inspection systems produce X-ray images of the highest quality. In addition to air-cooled monoblocks, they also use water-cooled metal-ceramic tubes with beryllium windows. Diode line and camera detectors with HD-TDI technology serve as sensors.

The requirement for operating X-ray inspection systems is that it must be possible to space the products to be inspected at the required distance from each other. Only a few X-ray inspection systems, like the SC-series from WIPOTEC-OCS, are inherently capable of creating the product gaps needed for the inspection. The products detected as defective during the inspection are removed from the current product flow with the aid of a large number of optionally available ejection mechanisms.

With optimum adjustment, it is then possible to achieve a false reject rate approaching zero – even with high product numbers and high speeds. The sensitivity of the WIPOTEC-OCS X-ray scanners is so high that they can detect even very small foreign bodies in the product.

X-ray inspection systems: Intelligent image processing

The success of an X-ray scanner is based largely on the use of powerful software routines combined with high-resolution X-ray images. The software relies on two parameters: grey values and contrast. Grey values represent the differing density of the products inspected. The second parameter is the contrast, which is understood to mean the comparison of a value with its neighbouring cells.

The support provided by X-ray scanners for the processing operations even goes a step further; by determining the density of cheese bars, the information obtained from the density profile can be used to keep the weight of individual cheese slices constant despite the presence of holes. They help to optimise the filling quantity, reduce overfilling costs and prevent underfilling.

Intelligent image processing supports the following tasks depending on the food sector:

X-ray inspection using top-down X-ray scanners

Top-down X-ray scanners inspect the product from above and for this the camera taking the image is located underneath the conveyor belt. This construction is always chosen when the height of the products is low compared to their surface area.

Top-down X-ray scanners are used even when the raw material is present in the form of bulk goods (rice, raisins, cereals). Multiple flap systems in the WIPOTEC-OCS X-ray scanners reduce the amount of material ejected with the foreign bodies into a collection box to the technical minimum by interrupting and diverting the product flow on only one track for a short time. This design saves over 80% of the good product which would otherwise be separated out with the foreign bodies.

X-ray inspection using side-view X-ray scanner

Side view X-ray scanners generate vertically aligned images. Cans and PET bottles are inspected parallel to the base, jars and bottles at a sharp angle.

The challenge actually starts one step before this. The containers to be inspected differ in height and it must be possible to adjust an inspection machine to accommodate this. Advanced WIPOTEC-OCS Side-View X-ray scanners solve this task automatically by product-dependent positioning of the X-ray tube. The X-ray source and detection unit are thus optimally aligned with the product. The beam runs through the bottom and you can also see foreign objects directly in this area.

Here, WIPOTEC-OCS offers two different combination solutions tailored to the application. Both are based on X-ray inspection, expanded either by the checkweigher component or by an optical inspection system. The result in both cases is an extremely space-saving combination of two complementary inspection techniques in one system.

The SC-W inspection system is a combination of X-ray inspection and checkweigher, operated via a common user interface. This inspection system with a maximum output of 300 packages a minute is also available as a multi-lane version. The products are not only examined for foreign bodies but are additionally subjected to a high-precision weight check. Units with incorrect weight are ejected into a separate container.

The SC-V inspection system is a compact combination of X-ray scanner and optical inspection system. In addition to use in traditional application areas of foreign body detection, the second inspection unit also allows optical checking of the products from above and/or below.

This enables checking of information printed on the products, as well as the positioning and readability of labels. Since operation without curtains is possible, this combination system is particularly suitable for lightweight products such as mini cakes, biscuits or brownies.

Product details of the inspection systems:

Quality assurance in the food industry: Early rejection of defective products

From a business point of view, it makes sense to carry out quality assurance of bulk goods, including rejection, at the earliest possible opportunity as only the purchase value of the raw material is lost rather than a saleable product.

X-ray scanners for lumpy products, such as meat cutlets, require differing ejection systems which have to work as efficiently in high-speed mode as flap systems.

These are either discharge belts designed as retraction belts on which products drop out of the product flow through an opening created between two conveyor belts, or those which can eject products within the system via a special reversing operation. These ejection mechanisms are particularly space-saving as defective products are discharged into a side container that fits underneath the inspection system.